The present invention relates to a drum or barrel suitable for use in the high-grade music boxes.
Because high-grade music boxes are constructed so that the internal structure can be seen from the outside, it is required that the internal structure be excellent in design. Also, to produce a graceful tune by using a chord and to allow playing of a plurality of musics by shifting the drum in the axial direction, it is necessary that pins distributed on the peripheral surface of the drum be slender in the order of 0.3-0.4 mm in diameter and the number of pins per unit area on the drum periphery be increased.
A conventional drum of a high-grade music box is produced through processes of drilling fine holes in a pipe made of brass and the like treated to bear an excellent aesthetic appearance, implanting the pins into the holes one by one, and filling up the pipe with rosin for purpose of reinforcing the pins and increasing the weight of the drum. Therefore, the conventional drum of the high-grade music box has the drawback that the process of implanting the pins is time-consuming, is inferior in work efficiency, and requires a high degree of skill. In addition, faults will be caused in final products.
On the other hand, another type of the drum for use in an ordinary music box is produced by pressing a flat plate to form pin-like projections and then bending the plate into a cylindrical shape. This makes it possible to ensure a mass-productivity and a desirable quality of the products. However, in such a conventional drum produced by the stamping, because the size of the pin is in the order of 0.6 mm in diameter at best and the proximal end of each pin is larger in size due to a removing work of a metal mold, the number of pins per unit area cannot be increased. Furthermore, in case that the switching of musics is achieved through movement of the drum, the length in the axial direction of the drum is elongated and the distance of movement in the axial direction of the drum must be increased, causing a problem in practice. Also, because the proximal end of each pin is larger in size as described above, if the pins are ground so that respective distal ends of the pins are included by one common cylindrical surface, the pin's length and diameter at the tip are varied over a number of pins and a desired timing of sound generation for a chord is not obtained; thus, this type of drum is not suitable for music boxes having a number of pins and reeds. Moreover, at the time of shaping the plate into the cylinder after the stamping, elongations in the axial direction and in the circumferential direction present, so that a positional precision of the pins cannot be obtained and a discrepancy occurs between the pin and a corresponding vibration reed, thus, this type of drum is also unsuited to the high-grade music box.
Furthermore, if the plate with a number of pins formed thereon by the stamping is shaped into the cylinder by use of a method similar to the conventional method, the elongations take place in the axial and circumferential directions. Specifically, the amount of elongation in the circumferential direction differs between the end portions and the midway portion of the plate and because end plates are pressed against the both ends of the cylinder after the cylindrical shape is completed, the midway portion expands in the radial direction and a gap appears at the midway portion. FIGS. 4 and 5 show the state of occurrence of the foregoing gap. As shown in FIG. 4, a flat rectangular plate material 1 which is produced by punching a plate into a configulation surrounded by four straight sides is formed with a large number of pins 2 through the pressing and, as shown in FIG. 5, this rectangular plate material 1 is shaped into a cylinder with its outer peripheral surface having the pins thereon. In this process, a gap 10 presents, as described above, at a midway portion of butting margins of the cylinder. If this type of drum is to be employed in the high-grade music box, the remaining of the gap 10 poses a serious problem in producing the high-grade music box because in general the whole internal mechanism of the high-grade music box is observable from the outside and has to be seen beautiful. In addition, if rosin or resin is filled within the drum and is solidified in order to enhance the tone quality, rosin and the like would flow out through the gap 10 in case it exists. Incidentally, in the experiment with the drum which was 95 mm long in the axial direction, there resulted in the gap 10 of 0.2 mm or so.